Brain injured patients are at high risk for forming blood clots in the legs and lungs. For non-brain injured trauma patients, we decrease the chances of these blood clots forming by placing the patients on a low dose of the blood thinner enoxaparin. Starting patients with a brain injury on the blood thinner is problematic, however, as this can theoretically cause the brain injury to worsen. Trauma surgeons wait a variable period of time before starting this blood thinner because waiting too long can result in the formation of these blood clots in the legs and lungs. Previous research has shown that some brain injuries which are of lower severity can have enoxaparin started at 24 hours after injury if the brain injury is stable on a repeated computed tomography (CT) scan of the head. This is a pilot study designed to look at the rates of worsening of brain injury if the low dose blood thinner is started at 24 versus 96 hours post-injury.